The present invention relates generally to amplifiers for use in base stations of a cellular telephone system or the like, and more particularly to an amplifier capable of improving the efficiency of Doherty amplifier circuitry.
Traditionally, in the case of electrical power amplification of a code division multiple access (CDMA) signal or a multi-carrier signal, a common amplifier is added a distortion compensation means for expanding the operation range of this common amplifier up to a nearby area of the saturation region to thereby lower electric power consumption. The distortion compensation means includes a feed-forward distortion compensation technique, pre-distortion compensation technique or else; however, with mere use of such distortion compensation, the achievability of lower power consumption reaches almost a limit. For this reason, in recent years, a specific type of amplifier circuitry, called the Doherty amplifier, draws attention as a high efficiency amplifier.